Recombinant DNA and related technologies will be used to study systematically expression of heterologous proteins in E. coli and yeast. The principal investigator and coworkers have developed a series of methods for expressing eukaryotic genes in coli (Guarente et al., 1980a) and have constructed E. coli strains that produce SV40 t antigne (Roberts et. al., 1979b), rabbit beta-globin (Guarente et al., 1980a), and, most recently, biologically active human fibroblast interferon (Taniguchi et al., 1980a). Genetic experiments will search for mutants that increase expression of IFN-beta in bacteria. Analysis of these mutants will likely clarify our understanding of the factors governing gene expression, both heterologous and homologous, in bacteria. We will attempt to use our methodologies to obtain heterologous gene expression in yeast. We have begun and will continue analysis of certain yeast promotors and regulatory genes that will expedite the expression experiments and will use our genetic techniques to search for expression mutants of yeast. Among the genes to be expressed in coli and yeast are: src from Avian sarcoma virus, the three T antigen genes of ployoma virus and the T antigen gene from SV40 virus, certain early genes of adenovirus, and the GAL4 gene of yeast.